此函数是通用的快速傅里叶变换C语言函数，移植性强，以下部分不依

赖硬件。此函数采用联合体的形式表示一个复数，输入为自然顺序的复

数（输入实数是可令复数虚部为0），输出为经过FFT变换的自然顺序的

复数

-This function is a generic fast Fourier transform C language function, strong transplantation, the following section is not dependent on hardware. This function takes the form of a complex number of the Commonwealth, the input is a natural sequence of complex numbers (input can make a real number is the imaginary part of complex number is 0), the output is the natural order of the FFT transform complex